Goes fast, possibly to scare (5)
I believe the answer is:
races
'goes fast' is the definition.
'races' can be an answer for 'goes' (racing is a kind of going). I'm not sure about the 'fast' bit.
'possibly to scare' is the wordplay.
'possibly' is an anagram indicator.
'scare' anagrammed gives 'RACES'.
Can you help me to learn more?
(Other definitions for races that I've seen before include "Goodwood events" , "Events at Epsom or Ascot?" , "Operates at excessive speed" , "Runs" , "Speed competitions for various peoples" .)